Tissue biopsy is typically intended to find the most malignant tissue when cancer is suspected, so as to have an accurate diagnosis of the overall tumor, determine the patient's prognosis and/or obtain information to guide treatment decisions. Typically, a biopsy needle is introduced through the skin (or in the case of brain biopsy, a small hole is drilled into the skull) and is inserted to the depth of the suspected disease site. A tissue sample is drawn into the needle through a window at the needle tip using mechanical or pneumatic action.
Obtaining the sample of tissue accurately often requires image guidance and/or a stereotactic technique to localize the biopsy needle's sampling window to the desired biopsy location within the patient. Image guidance may be provided by a computed tomography (CT) or magnetic resonance imaging (MRI) scan. Even with such image guidance, the biopsy that is acquired may not be fully representative of a patient's disease state. Performing a biopsy of a glioma is an example illustrating this difficulty. A typical goal of glioma biopsy is to identify the most malignant (that is, the highest grade) sample; however, this is often complicated by the fact that gliomas by nature are spatially heterogeneous. Even with the aid of an MRI or CT scan to identify the gross location of the brain tumor, it is often difficult to acquire a biopsy representing the most malignant part of the tumor without further guidance. Further, such external imaging techniques may not provide sufficient spatial resolution to accurately determine whether the biopsy device is appropriate positioned at a desired biopsy target. For example, the spatial resolution of MRI may be on the order of a few mm, which may be insufficiently fine.
In situations such as a glioma biopsy, or other situations, more than one biopsy attempt may be required to acquire an elusive piece of tissue. This takes time and may be increasingly risky as more biopsies are taken, particularly for sensitive sites such as the brain. As well, since there is often a limit to the number of biopsies that a surgeon may acquire safely, there is typically more risk of missing critical tumor zones (i.e., under-estimation of malignancy) compared with open surgical acquisition of tissue.
There is also the issue of safety during these biopsy procedures. For example, if a large blood vessel is situated within the tissue sampling volume, there is risk of the surgeon tearing a part of the vessel during biopsy excision and so causing local hemorrhage.